1. Field of the Invention
The invention relates to a ventilator to be connected to the airways of a human or of an animal for supplying and emitting respiratory gas to and from the airways, according to a predetermined pattern, which is dependent on at least one parameter, the ventilator having an analog control unit, which, depending on the parameter, regulates the supplying and/or the emitting of the respiratory gas so that a predetermined pattern is substantially maintained.
The invention also relates to a ventilator, of the type having several functional units, which enable the ventilator to supply and/or emit respiratory gas following a predetermined pattern, and a microprocessor which controls and/or supervises at least one of the functional units.
2. Description of the Prior Art
A known ventilator (Servo Ventilator 900C, Gebrauchsanweisung Publ. No. AG 11884, October 1988) has an expiration section with an expiration valve, which opens and closes by means of an electromagnet. Thereby, a desired pressure can be maintained in the expiration section of the ventilator. The electromagnet is controlled by an analog control unit which, depending on the existing air pressure, controls the position of the expiration valve. The advantage of the analog control unit is that it quickly adjusts to the desired regulation level, but it is not very accurate for maintaining a constant desired pressure.
Another known ventilator (7200 Series Microprocessor Ventilator, Puritan Bennett, Form No. AA-213, May 83) has a microprocessor that controls and supervises substantially all functions of the ventilator. For example, the pressure in the expiration section may be maintained with high accuracy at the desired value. On the other hand, the complexity of the system slows down a desired change of the pressure in the expiration unit because the microprocessor moves towards the new position of equilibrium at a slow pace. Further, the ventilator is extremely vulnerable. If the microprocessor would cease to function for any reason, the functional units of the ventilator will then also cease to operate, and the result may be injurious or fatal for a patient connected to the ventilator.